1. Field of the Invention
The present invention relates to an apparatus for manufacturing semiconductors used in integrated circuits, optoelectronic devices and the like.
2. Description of the Prior Art
In the prior art, the plasma process has been used for the low temperature production of semiconductors used in integrated circuits optoelectronic devices and the like. However, it has been impossible to avoid radiation damage caused by the high energy particles, such as ions and electrons, that are generated by the plasma process. This has led in recent years to the use of a photo-excitation process, a non-damage process that utilizes a photochemical reaction. The photo-excitation process is a technique whereby optical energy is used to excite a reaction gas and promote a chemical reaction for gas phase growth, etching, doping and ashing, for example. The photo-excitation process consists of a reaction chamber and a light source constituted of, for example, a lamp (for example, a mercury lamp, mercury-xenon lamp, deuterium lamp, xenon lamp, inert gas lamp or rare gas lamp) or a laser (for example, an excimer laser, argon laser, CO.sub.2 Laser, dye laser YAG laser or free electron laser) and synchrotron radiation, and is configured so that light from the light source is led to the reaction chamber via appropriate optical elements, such as mirrors and lenses, to excite the reaction gas and promote a chemical reaction. The photo-excitation process can enable the reaction to proceed at a low temperature, even at room temperature. Compared with other methods there is very little radiation damage, and by selecting an appropriate wavelength the reaction can be performed with no damage.
Conventional arrangements for photo-excitation processes are shown in FIGS. 8 and 9. In FIG. 8, numeral 2 denotes a gas reaction chamber and 3 a light transmitting window provided at the top part of the gas reaction chamber 2. A light source is provided above the light transmitting window 3. A reaction gas inlet 7 is provided in the side wall of the gas reaction chamber 2. A substrate holder 8 is attached inside the gas reaction chamber 2 by an appropriate means (not shown). Numeral 9 denotes a substrate which is placed on the substrate holder 8. An exhaust outlet 10 is provided at the lower part of the gas reaction chamber 2 and is connected to a vacuum pump. A window-spray gas inlet 23 is provided in the upper side wall of the gas reaction chamber 2 with the supply opening pointing upward at an angle. In the example of the conventional configuration shown in FIG. 8, the light emitted by an external light source passes through the light transmitting window 3, which shuts off the atmosphere, and excites the reaction gas introduced via the reaction gas inlet 7 provided in the side wall of the gas reaction chamber 2, whereby a photochemical reaction takes place on the substrate 9 in the gas reaction chamber 2. However, because the reaction gas is also in contact with the lower surface of the light transmitting window 3, the reaction gas also produces a photochemical reaction on the lower surface of the light transmitting window 3. The reaction gas which has completed the chemical reaction is evacuated to the outside by a vacuum pump via the exhaust outlet 10.
With reference to FIG. 9, a light source chamber 21 is formed in the upper part of the gas reaction chamber 2. A light source 11 is attached inside the light source chamber 21 by an appropriate means (not shown). A mirror 12 is attached by an appropriate means (not shown) between the light source 11 and the top face of the light source chamber 21. A purge gas inlet 22 is provided in the side wall of the light source chamber 21. An exhaust outlet 10 is provided in the side wall of the light source chamber 21 opposite to the side wall in which the purge gas inlet 22 is provided. Elements denoted by reference numerals 3, 7, 8, 9, 10 and 23 in the gas reaction chamber 2 at the lower part of the light source chamber 21 have the same arrangement as that shown in FIG. 8.
In the example of the conventional configuration shown in FIG. 9, direct light from the light source 11 provided in the light source chamber 21 in which gas is replaced by purge gas introduced via the purge gas inlet 22, and light reflected by the mirror 12, pass through the light transmitting window 3 and excite the reaction gas introduced via the reaction gas inlet 7 provided in the side wall of the gas reaction chamber 2 and produces a photochemical reaction on the substrate 9 in the gas reaction chamber 2. However, as in the case described above, because the reaction gas is also in contact with the lower surface of the light transmitting window 3, the reaction gas also produces a photochemical reaction on the lower surface of the light transmitting window 3.
In the case of each of the arrangements shown in FIGS. 8 and 9, a photochemical reaction is produced on the lower surface of the light transmitting window 3 that results in the contamination of the lower surface of the light transmitting window 3. As the film of contamination becomes thicker it limits the amount of light that is transmitted from the light source to the gas reaction chamber 2, thereby inhibiting the photochemical reaction in the gas reaction chamber 2. Described below are conventional methods used to prevent such a film forming on the light transmitting window 3.
1. Spraying inert gas on the light transmitting window 3 (with reference to FIGS. 8 and 9, the spraying on the light transmitting window 3 with inert gas from the gas inlet 23).
2. Coating the light transmitting window 3 with a fluoride oil.
3. Inserting a heavily perforated quartz plate or a teflon film winder under the light transmitting window 3.
However, these methods have the following problems. In the first method in which inert gas is sprayed on the light transmitting window 3, spraying a large amount of inert gas onto a light transmitting window 3 with a large area produces turbulence that makes it impossible to avoid reaction gas being drawn in, which results in the deposition of the said film on the light transmitting window 3. In the case of the second method in which the light transmitting window 3 is coated with a fluoride oil, because the fluoride oil is decomposed by the light, over long periods of use (for example 30 min.) it is not able to prevent the deposition of the film on the light transmitting window 3. In the case of the third method which involves inserting a heavily perforated quartz plate or a teflon film winder under the light transmitting window 3, the overall amount of transmitted light is reduced and the size of the apparatus is increased.